1. Field of the Invention
The present invention relates to phase control in a variable valve mechanism of an internal combustion engine.
2. Description of the Related Art
A variable valve mechanism in which a cam shaft that operates an intake valve and an exhaust valve provided for each cylinder, is of a double shaft structure with an outer cam shaft on the outer side and an inner cam shaft on the inner side arranged within this outer cam shaft, and a main cam is attached to the outer cam shaft while a sub cam is attached to the inner cam shaft, is known from the disclosure of Japanese Laid-open (Kokai) Patent Publication Application No. 2002-054410 (Patent Document 1) and Japanese Laid-open (Kokai) Patent Publication Application No. 2009-144521 (Patent Document 2). This type of variable valve mechanism is provided on either one or both of an intake valve and an exhaust valve, and the phase of a cam is appropriately changed to thereby variably control the operating timing from the valve open timing to the valve closed timing.
Normally, the outer cam shaft in a variable valve mechanism determines the phase of the cam with respect to the crank shaft angle, and the inner cam shaft adjusts the phase of the sub cam with respect to the main cam to determine phase shift between the sub cam and the main cam. By controlling the phase of the main cam and the sub cam in this manner, the valve open timing and the valve close timing are each advanced or retarded, thereby enabling variable control of the length of an open period from the open timing to the close timing (operating angle).
As described above, in a variable valve mechanism that performs phase control of the main cam and the sub cam with a cam shaft of a double shaft structure, in a case in which a locking (seizing) defect occurs in either one of the outer cam shaft and the inner cam shaft, efficient operation of the internal combustion engine may be influenced in some cases. That is to say, for example in a variable valve mechanism provided for an intake valve, if the outer cam shaft of the main cam is locked at an advanced angle position, the overlapping between the exhaust valve and the intake valve (a period in which both of the valves stay open) is maintained great. As a result, there is a possibility that a phenomenon of increasing residual gas at the time of idle operation may occur, leading to an undesirable situation such as unstable combustion.
In view of the above points, it is an object of the present invention to provide an apparatus and a method for controlling a variable valve mechanism in an internal combustion engine, that is capable of executing fail safe control in a case in which locking occurs in either one of the cam shafts.
In order to achieve the above object, the apparatus (method) for controlling a variable valve mechanism in an internal combustion engine according to the present invention is configured as described below.
The variable valve mechanism has a cam shaft of a double shaft structure including an outer side cam shaft and an inner side cam shaft, and a cam is attached to each of these outer and inner cam shafts, such that it is possible to adjust the phase of the cam of one of the cam shafts with respect to the cam of the other cam shaft. By means of a pair of these cams, at least one of a pair of intake valves and a pair of exhaust valves of an internal combustion engine is operated.
The control apparatus (method) includes the following.
a current phase determination section for or step of determining, when an abnormality is detected in one cam shaft of the pair of cam shafts, the current phase of the cam of the abnormal cam shaft; and
a phase control section for or step of controlling the phase of the cam of the other cam shaft, in accordance with the determined current phase of the one cam.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawing.